Coating and filler compositions comprising platy layered silicate pigments

ABSTRACT

A coating composition comprising platy magadiite pigment(s); a paper product comprising platy magadiite pigments; and an aqueous suspension comprising platy magadiite and a suspending agent selected from the group consisting of; polyacrylate polymers, polyvinylalcohol polymers, maleic anhydride-containing copolymers, and polyphosphates, and a latex dispersion or emulsion of latex polymers selected from the group consisting of styrene butadiene polymers, acrylic polymers, carboxylated acrylonitrile: butadiene polymers, polyvinylchloride, polyvinyledenechloride, polystyrene, fluorinated polyethylene and polypropylene, and polytetrafluoroethylene; and an article or formulation comprising a platy layered silicate.

BACKGROUND OF THE INVENTION

This invention relates to coating compositions and end-use applicationsthereof.

Paper is usually coated to enhance its aesthetic properties. Paperpigments are an integral part of modern paper coating and surface sizingtechnology. It is well known in the paper industry that a wide varietyof pigments, such as titanium dioxide, calcium carbonate, talc,synthetic silicates, and clays such as bentonite and kaolin, aresuitable for use as paper fillers and/or coatings. Kaolin, a naturallyoccurring hydrated aluminate silicate, is presently the most widelyutilized and is available in a range of particle sizes and brightnesses.

Surprisingly little use is made by the paper industry of inorganicpigments based on silica or silicates, excluding kaolin clays. Silicaand silicates and other pigments, such as TiO₂, comprise less than 3percent of the paper pigments. High-structure amorphous silica pigmentshave been used in the paper industry to replace TiO₂, at least in part,or to improve ink receptivity. See, for example, G. Alderfer and R.Crawford, Chapter 12—“High Structure Amorphous Silica Pigments inPaper”, in Pigments for Paper/edited by R. W. Hagemeyer, TAPPI PRESS1997.

It would be desirable to provide a new class of synthetic paper pigmentsbased on silica or silicates and having a combination of features thatare desirable to produce high quality paper products for the printing,food packing, and other industries.

SUMMARY OF THE INVENTION

In a first aspect, the present invention is a coating compositioncomprising platy magadiite pigment(s).

In a second aspect, the present invention is a coating compositioncomprising a mixture of platy magadiite pigment(s) with another pigmentselected from the group consisting of calcium carbonate, precipitatedcalcium carbonate (PCC), kaolin, talc, alumina trihydrate, and titaniumdioxide.

In a third aspect, the present invention is a paper product comprisingplaty magadiite pigments.

In a fourth aspect, the present invention is an aqueous suspensioncomprising platy magadiite and a suspending agent selected from thegroup consisting of polyacrylate polymers, polyvinyl alcohol,polyphosphates and copolymers of styrene and maleic anhydride resins andother copolymers of maleic anhydride.

In a fifth aspect, the present invention is a suspension comprisingplaty magadiite, a suspending agent, and a latex polymer or binderselected from the group that includes, for example, styrene-butadienelatex, styrene-acrylate latex, styrene-butadiene-acrylonitrile latex,styrene maleic anhydride latex, styrene-acrylate-maleic anhydride latex,polysaccharides, proteins, polyvinyl pyrrolidone, polyvinyl alcohol,polyvinyl acetate, cellulose and cellulose derivatives.

The term “latex polymer” means herein a colloidal dispersion of apolymer in water comprising a cationic, anionic or nonionic polymerdispersed in the aqueous phase and an emulsifying agent.

In a sixth aspect, the present invention is a coating compositioncomprising layered silicates pigments selected from the group consistingof platy magadiite, platy kenyaite, platy octasilicate, platy KHSi₂O₅,platy Na₂Si₂O₅ platy talc, platy CaCO3, platy bentonite, platy mica,platy satin white, platy vermiculite and other platy pigments.

Other aspects of the present invention will become apparent from thefollowing detailed description and claims.

As used herein, the term “platy magadiite” means a crystalline sodiumsilicate with a platy morphology comprising substantially flat plateswith lateral dimensions [length and width] of from 0.2 to 10 microns,more preferably, from 0.5 to 5 microns and, most preferably, from 1 to 2microns.

As used herein, the term layered silicate” means an inorganic material,such as a smectite clay mineral, that is in the form of a plurality ofadjacent, bound layers and has a thickness, for each layer, of about0.03 micron. to about 0.5 micron, preferably about 0.1 micron.

DETAILED DESCRIPTION OF THE INVENTION

Preferably, the platy magadiite employed in the practice of the presentinvention is a synthetic magadiite comprising more than fifty percent byweight of platy magadiite, more preferably, more than eighty weightpercent and, most preferably, more than ninety weight percent by weightof platy magadiite

Platy magadiite can be produced from water glass (water soluble sodiumsilicate), water and sodium hydroxide (NaOH) under hydrothermal orsub-hydrothermal conditions to yield a crystalline product having platymorphology with crystals resembling flat glass plates of from about 0.2to about 10 microns in length and from about 0.1 to about 0.1 microns inthickness. The product is produced as a white powder and the platymorphology is ideally suited to produce white and very smooth coatingson paper.

The surface of platy magadiite can be made more or less hydrophilic orhydrophobic by adjustment of the sodium content via titration withinorganic or organic acids and/or by treatment with organic surfactants.These treatments can be used also to tune up the surface acid or basiccharacter. Moreover, it is possible to introduce a variety of functionalgroups on the platy magadiite surface by reaction of surface silanol(Si—OH) with numerous chemicals to produce functional surface groups(Si—OR), which may facilitate the interaction of the platy magadiitepigment with the cellulose fiber matrix.

Platy magadiites can be modified with reactive organic coupling agents,such as, for example, organosilanes, alcohols and quaternary salts, toprovide paper products with unique surface properties, such as, forexample, optical and adhesive properties.

Platy magadiites and their method of preparation are described in detailin copending U.S. application Ser. No. 10/257,487, incorporated hereinin its entirety by reference.

The platy magadiite pigments of the present invention can be used in avariety of applications such as, for example, nanofiller in polyolefinnanocomposites, paint pigment formulations, catalyst support [Zieglerand Metallocene] for polyolefin catalysts, dye stabilization for use inplastics or in textile fibers containing dispersed dye-magadiite pigmentparticles and the like.

The platy magadiite pigments can be used also in making (a) paperproducts comprising platy magadiite in combination with polymer films inbilayer or multilayer articles, b) latex products comprising magadiitein applications other than paper, such as paints and films for roadsigns, c) cardboard products, d) ink products, e) magadiite-latexadditives to FR (flame retardant) formulations, f) magadiite modifiedwith reactive organic coupling agents, such as organosilanes, alcohols,quaternary salts, etc. to provide paper products with unique surfaceproperties, such as, for example, optical and adhesive properties.

The platy magadiite pigments can be used also in combination withbinders, such as latex, starch and co-binders such as carboxy methylcellulose (CMC) and other additives, including lubricants andsurfactants, rheology modifiers and dispersing agents used to make papercoatings.

The platy magadiite pigments can be used also in the paper makingprocess as a filler.

In general, the paper coating composition of the present invention canbe prepared by dispersing the magadiite pigment in deionized water.

The amount of platy magadiite pigment used depends on the desired papercoating performance including sheet gloss, ink gloss, brightness,opacity, Helio, roughness, CIE whiteness, B-value, and the like; therelative amounts of other pigments such as calcium carbonate, kaolin,titanium dioxide; and the relative amounts of other components such aslatex, surfactants and dispersing agents.

In general, the platy magadiite pigment is used in an amount of fromabout 0.1 wt. percent to about 30 wt. percent, more preferably, fromabout 1 wt. percent to about 30 wt. percent and, most preferably, fromabout 3 wt. percent to about 30 wt. percent, based on the weight of thepaper composition comprising base paper or raw stock, paper pigment, andbinder.

Advantageously, the platy magadiite pigments are suspended in waterusing suspending agents to disperse and stabilize the platy particles atconcentrations and viscosities suitable for application as coatings onpaper.

The suspending agents which can be employed in the practice of thepresent invention include, for example, polyacrylate polymers, such as,for example, DISPEX™ N40, a salt of a polymeric acid in aqueoussolution, a product of Allied Colloids Inc., polyvinyl alcohol, such as,Polyvinyl Alcohol 103, a product of Air Products, polyphosphates, suchas potassium tripolyphosphate, sodium hexametaphosphate, tetrasodiumpyrophosphate, and copolymers of styrene and maleic anhydride resins andother copolymers of maleic anhydride.

The preferred suspending agents are polyvinyl alcohol, polyacrylate andmaleic anhydride-containing copolymer resins, and polyphosphates. Themore preferred suspending agents are polyvinyl alcohols, polyacrylateand polyacrylate copolymers. The most preferred suspending agents arePolyvinyl Alcohol 103 and Dispex™ N40.

The amount of suspending agent employed in the practice of the presentinvention depends on the desired solids content in the pigmentdispersion and on the solids composition. In general, the suspendingagent is used in an amount of from about 0.01 wt. percent to about 2.0wt. percent, more preferably, from about 0.05 wt. percent to about 1.0wt. percent and, most preferably, from about 0.05 wt. percent to about0.5 wt. percent, based on the weight of the pigment in the composition.

Preferred latex polymer dispersions or binders which can be employed inthe practice of the present invention include, for example, carboxylatedstyrene-butadiene latex, carboxylated styrene-acrylate latex,carboxylated styrene-butadiene-acrylonitrile latex, polyvinyl alcohol,and carboxylated copolymers of polyvinyl acetate and acrylate esterlatex.

Polysaccharides which can be employed in the practice of the presentinvention include, for example, agar, sodium alginate and starchincluding modified starches such as thermally modified starch,carboxymethylated starch, hydroxyethylated starch and oxidized starch.

Examples of proteins that can be suitably used in the practice of thepresent invention include albumin, soy protein and casein.

The magadiite pigment of the present invention can be used in a varietyof other applications such as, for example, nanofiller in polyolefinnanocomposites, paint pigment formulations, catalyst support [Zieglerand Metallocene] for polyolefin catalysts, dye stabilization for use inplastics or in textile fibers containing dispersed dye-magadiite pigmentparticles and the like.

The following working examples are given to illustrate the invention andshould not be construed as limiting its scope. Unless otherwiseindicated, all parts and percentages are by weight.

The terms used in the Examples are defined as follows: DISPEX ™-N40 Saltof a polymeric acid in aqueous solution, a product of Allied ColloidsInc. Cowl ™ Mixer A high shear mixing system used to disperse thepigment and produce a stable slurry. This device is made by MorehouseIndustries, Inc. CP 638NA Carboxylated styrene/butadiene latex, aproduct of The Dow Chemical Company. FINNFIX ®10 Carboxymethylcellulose, a rheology modifier. FINNFIX 10 is a registeredtrademark of Metsaeleeton. RAP ™ 501NA CarboxylatedStyrene/butadiene/acrylonitrile latex, a product of The Dow ChemicalCompany. Roto base A paper that is coated with a paper pigment andbinder package that is suitable to be printed using the Roto Gravureprinting process. Dow Bench A table bench scale coater to Blade coaterapply the paper coating formulation to the paper and uses a blade todoctor the excess coating to produce a smooth coated surface.

EXAMPLE 1 Roto Gravure Coating Formulation

1) Pigment Dispersion

The pigment was dispersed in deionized water at 43 percent solids using0.25 parts of a dispersant, Dispex-N40, based on 100 parts dry pigment.The dispersant was added to the water and then the platy magadiitepigment was slowly added while mixing with a Cowl Mixer. The agitationrate was increased when all the platy magadiite pigment is added to thewater, and the platy magadiite pigment was left to mix for 15 minutes.

2) Paper Coating Formulation

Several paper coating formulations were prepared by mixing the differentcomponents for each coating formulation in the order that they appear inTable 1. The rheology modifier, carboxy methylcellulose (Finnfix 10) wasadded to provide some thickening to achieve the required coat weights.The formulations were prepared at 51 percent solids and the pH wasadjusted with NaOH to 8.5.

3) Preparation of Samples

The paper coating formulation was applied using the Dow Bench Bladecoater. The coatings were applied on a wood containing Roto base paper.The target coat weight was 4.5-lbs/3300 sq. ft.

The coated paper samples were then supercalendered using a standard labscale super calender. The control, which is formulation 1, wascalendered to target gloss at 1500 pounds per lineal foot (phi) and 67°C. The same super calender conditions were then used for all othercoating systems.

The paper samples were then left to condition to constant moisturecondition before testing. The samples were then tested for keyproperties including optical and print performance. The results areshown in FIGS. 1-8. Test Procedures 1. Sheet Gloss TAPPI Test Method -T480 2. Ink Gloss^(A) 3. Brightness TAPPI Test Method - T646 4. OpacityTAPPI Test Method - T425 5. Helio^(B) 6. Roughness TAPPI Test Method -T555 7. Whitenesss TAPPI Test Method - T-560 8. CIE B-Value TAPPI TestMethod - T-560 9. Coated Paper Strength TAPPI Test Method - T514^(A)Ink Gloss Test ProcedureA thin ink film is applied to a strip of paper using a PrufbauPrintability tester and then the ink is allowed to dry at roomtemperature. The printed samples are then measured for ink gloss (PrintGloss) using the same procedure as in T480. The only difference is theapplication of the ink film using the Prufbau. The Prufbau PrintabilityTester is a product of Prufbau Company in Germany.^(B)An Helio Test ProcedureAn ink film is applied using a Reprotest I.G.T. ACII 5 PrintabilityTester product of IGT, and Heliotest Kit. The ink is applied to thepaper using an engraved wheel following the procedure described below.When the ink is transferred from the engraving of the wheel to thepaper, sometimes ink does not transfer from some of the cells orengravings.# This will result in a missed ink dot on the printed paper. Thisphenomenon is referred to as a missing dot. The number of missing dotsin a 20 mm length of a printed strip of paper is used as a measure toquantify the quality of the Roto print. The higher the number of themissing dots, the lower the print quality. An optimal number is 0missing dots.Procedure:1. Replace cardboard backing on IGT with green rubber backing and MylarFilm from Heliotest kit.2. Place support-holder plate into upper IGT slot. Attach beveled bladeto weight arm and slide onto plate. Adjust plate so that the blade restsaligned on the Heliotest wheel and tighten (plate should beapproximately vertical).3. Switch IGT to constant speed and set speed to 1.0 m/s remember to useconstant speed scale.4. Start with pressure (upper hub) of 50 kilogram force (kgf).5. Place 2 to 3 drops Heliotest ink onto engraved wheel with measuringscale and spin wheel clock-wise. Only engraved depressions should appeartinted against the shine of the chrome. (Heliotest ink is prepared bycutting gravure printing ink with N-butyl carbitol acetate to 75 cPbrookfield or 23 seconds with #4 Shell cup.) If streaking occurs, cleanwheel and IGT's beveled blade. Re-ink as needed to keep evendistribution in the depressions of the wheel.6. Stop wheel with the blade resting within 1 inch of the end of thewide band.7. Run a strip (strips need only be attached by the lead clip).8. Count missing dots in the inked band on strip from dark to light.Mark strip at 20 missing dots. This should fall approximately 60 to 70for the control then the rest of the samples are run at that condition.If it is out of this range, adjust pressure until it is reasonablyclose. (Raising pressure should raise the 20-dot mark).9. Run samples randomly. Measure distance in mm to the mark. The greaterdistance to 20 missing dots, the better the printability.10. Clean up with acetone.

TABLE 1 Paper Coating Formulation Total of 100 Parts Including PlasticPigment Formulations 1-10 PIGMENTS 1* 2 3 4* 5 6 *7 8 9* 10 Hydraprint100 85 75 100 85 75 Hydrocarb 90 100 75 100 75 Magadiite 15 25 15 25 2525 BINDERS/ADDITIVES Dry Parts per 100 parts Pigment Rap 501 6 6 6 6 6CP 638 6 6 6 6 6 Finnfix 10 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 AimPoints: % Solids 51% 51% 51% 51% 51% 51% 51% 51% 51% 51%*control

FIGS. 1-9 show that the use of Magadiite pigment in any formulation andwith any latex resulted in:

1) Better gloss and printed ink gloss.

2) Better brightness with pigment systems; clay and carbonate. Howevermore brightness improvement with the carbonate formulation.

3) Better opacity with both pigment systems and with both latexes.

4) Better Whiteness and more blue coating with both with all thedifferent systems.

5) Far better Hellio, which is a measure of Gravure, print quality. Thisimprovement was evident across all the systems.

6) Offset latex like CP 638NA demonstrated improved Roto printsperformance in the presence of platy magadiite-based pigment. This couldnot be done with traditional pigment systems.

7) The coated paper surface with platy magadiite appears to have ahigher binder demand as shown by FIG. 9. This suggest that coating madewith platy magadiite will require slightly more binder especially forthe offset printing process.

Although the invention is specifically described with respect to thepreferred embodiment, that is, platy magadiite, the present inventionalso encompasses other platy layered silicates, such as platyoctasilicate, platy kenyaite and related materials such as platyKHSi₂O₅, and platy Na₂Si₂O₅. These platy layered silicates typicallyhave a platy morphology comprising substantially flat plates which arefrom 0.5 to 10 microns long, and from 0.01 to 0.1 microns thick, or haveaspect ratios of from 5 to 1000.

1. A coating composition comprising platy layered silicate pigment(s).2. The coating composition of claim 1 wherein the layered silicatepigment(s) is present in an amount of from 0.1 wt. percent to 30 wt.percent, based on the weight of the composition.
 3. The coatingcomposition of claim 1 wherein the platy layered silicate is a syntheticmagadiite comprising more than fifty percent by weight of platymagadiite.
 4. The coating composition of claim 1 wherein the platymagadiite is a synthetic magadiite comprising more than eighty percentby weight of platy magadiite.
 5. The coating composition of claim 1wherein the platy magadiite is a synthetic magadiite comprising morethan ninety percent by weight of platy magadiite.
 6. The coatingcomposition of claim 1 wherein the platy layered silicate is selectedfrom the group consisting of platy magadiite, platy kenyaite, platyoctasilicate, platy KHSi₂O₅, and platy Na₂Si₂O₅.
 7. The coatingcomposition of claim 1 further comprising another pigment selected fromthe group consisting of calcium carbonate, precipitated calciumcarbonate (PCC), kaolin, talc, alumina trihydrate, titanium dioxide,platy talc, platy CaCO3, platy bentonite, platy mica, platy satin whiteand platy vermiculite.
 8. The coating composition of claim 3 wherein theplaty magadiite is modified with a reactive coupling agent selected fromthe group consisting of organosilanes, alcohols and quaternary salts. 9.A paper product comprising a coating prepared using the composition ofclaim
 1. 10. (canceled)
 11. (canceled)
 12. (canceled)
 13. A latexproduct comprising platy layered silicate pigments.
 14. The latexproduct of claim 13 wherein the platy layered silicate is a syntheticmagadiite comprising more than fifty percent by weight of platymagadiite.
 15. (canceled)
 16. (canceled)
 17. (canceled)
 18. (canceled)19. An aqueous suspension comprising a platy layered silicate, asuspending agent and a latex polymer.
 20. The aqueous suspension ofclaim 19 wherein the suspending agent is selected from the groupconsisting of polyphosphates, polyacrylate polymers, polyvinylalcoholpolymers, and maleic anhydride-containing copolymers.
 21. The aqueoussuspension of claim 19 wherein the platy layered silicate is a syntheticmagadiite comprising more than fifty percent by weight of platymagadiite.
 22. The aqueous suspension of claim 19 wherein the platylayered silicate is a synthetic magadiite comprising more than eightypercent by weight of platy magadiite.